Liquid dispensing systems are incorporated into many manufacturing production lines for dispensing a liquid onto a substrate. Certain liquid dispensing systems are configured for applying a pattern of a heated liquid, such as a thermoplastic material or a hot melt adhesive, to a continuously-moving substrate, such as a woven or non-woven web used in the manufacture of multilayer diapers and other multilayer hygienic products. To that end, liquid dispensing systems include one or more discharge passageways arranged to provide the pattern. Typically, the discharge passageways are located in corresponding nozzles removably attached directly or indirectly to a liquid distribution manifold. The flow of liquid from a liquid supply to the nozzle may be interrupted by a valve element of an intervening dispensing module for dispensing the liquid with a pattern.
Particles may be present in the liquid being dispensed from the discharge passageway. For example, liquids in hot melt adhesive dispensing  may include solidified, insoluble particles or char produced by operation of a melter providing the hot melt adhesive to the liquid dispensing system. Relatively small particles pass through the discharge passageway and are dispensed along with the liquid. Relatively large particles may become lodged in the discharge passageway and produce clogs. As a result, the discharge passageway is susceptible to partial or total obstruction by foreign debris that either reduces or prohibits liquid flow to the discharge orifice. Flow restriction may also arise from solidified liquid coating the wall surrounding the discharge passageway. Yet another source of particles is debris originating from solidified liquid residue produced during non-operational intervals, such as maintenance periods. This can adversely affect adhesive bonding and reduce product quality.
Conventionally, clogged discharge passageways in a nozzle are cleaned by halting the flow of product in the production line and removing the clogged nozzle from the liquid dispensing system. The clogged nozzle is disassembled and the discharge passageway is cleaned of debris. The reassembled nozzle is reintroduced into the adhesive dispensing system, adjusted and calibrated. The production line is then restarted. The cleaning process is time consuming and labor intensive. Moreover, because the production line is stopped to clean the nozzle, the process throughput is reduced.
What is needed, therefore, is a liquid dispensing system in which the discharge passageway of a nozzle can be cleared of obstructions without removing the nozzle from the dispensing system. 